What is wrong with this sorting code? Python

Question

So i'm supposed to take in a number n, add n numbers to a list, then sort the list and print.

numCol=int(input());
vals=[];
for x in range(numCol):
    vals.append(int(input()))

for x in range(len(vals)):
    curr=vals[x];
    for y in range(x+1,len(vals)):
        if(curr>vals[y]):
            temp=vals[y];
            vals[y]=curr;
            vals[x]=temp;
print(vals);

the code doesn't work properly. We haven't learned sorting algorithms thoroughly really yet, so i'm kinda just making my own, but it resembles selection sort I think. Anyways, why is it not printing the values in ascending order?

Edit: I input 4, then make list 4, 3, 2, 1. Output is [1, 4, 4, 4]

this is only making one pass through the list ... you need to continue until you make no swaps ... also you can swap in python with vals[x],vals[y]=vals[y],vals[x] — Joran Beasley
– Joran Beasley, Commented May 18, 2016 at 5:33
Are you required to implement a sorting algorithm? Because the practical answer would be to use the built-in Python sorting method(s). — deceze
– deceze ♦, Commented May 18, 2016 at 5:36
We have to make our own sorting algorithm, but it can resemble a premade algorithm. I'm basing this off of selection sort I think. How is it only making one pass? — Thandor7765
– Thandor7765, Commented May 18, 2016 at 5:38

delta · Accepted Answer · 2016-05-18 05:37:49Z

1

the problem is curr should change after swap.

for x in range(len(vals)):
    curr=vals[x];
    for y in range(x+1,len(vals)):
        if(curr > vals[y]):
            temp = vals[y]
            vals[y] = curr
            vals[x] = temp
            curr = vals[x] # <--

answered May 18, 2016 at 5:37

delta

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2 Comments

Thandor7765 Over a year ago

thanks! that did it! How would I incorporate curr, butt update accordingly?

delta Over a year ago

@DChalo according to your code, curr is the value of vals[x], so whenever vals[x] changes, update curr accordingly.

Samvel Petrosov · Accepted Answer · 2016-05-18 05:43:21Z

1

Change this part of code

 for x in range(len(vals)):
    curr=vals[x];
    for y in range(x+1,len(vals)):
        if(curr>vals[y]):
            temp=vals[y];
            vals[y]=curr;
            vals[x]=temp;

To this:

for x in range(len(vals)):
    for y in range(x+1,len(vals)):
        if(vals[x]>vals[y]):
            temp=vals[y];
            vals[y]=vals[x];
            vals[x]=temp;

answered May 18, 2016 at 5:43

Samvel Petrosov

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1 Comment

Thandor7765 Over a year ago

Sweet! Thank you so much

tfv · Accepted Answer · 2016-05-18 05:43:01Z

0

You can solve sorting of lists much easier and in a more pythonic way, simply use the sort command, here is an example:

import random

a=random.sample(range(30), 10)
print a
a.sort()
print a

answered May 18, 2016 at 5:43

tfv

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1 Comment

Thandor7765 Over a year ago

Thanks! It's just for this problem we couldn't use a built in algo

lightsong · Accepted Answer · 2016-05-18 06:12:43Z

0

You're welcome -

numCol=int(input());
vals=[];
for x in range(numCol):
    vals.append(int(input()))

for x in range(len(vals)):
    for y in range(x+1,len(vals)):
    if(vals[x]>vals[y]):
        temp=vals[y]
        vals[y]=vals[x]
        vals[x]=temp
print(vals)

The problem was that you weren't changing the value of cur to be compared correctly.

Edit - Just saw other answers had beat me to it :(

answered May 18, 2016 at 6:12

lightsong

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